Mag 20 PO Mod

[j4c11]

Got the flywheel off, good news,no crack in the block. Seal is dripping oil through a crack, that made it easy to identify where the oil was coming from . Anything else I should do while I have it apart? Should I replace the coil just because it's 30 years old? It works fine. What about the magnets on the flywheel, should I drop some extra JB weld on them?

[Justin Witt]

Originally Posted by j4c11

Got the flywheel off, good news,no crack in the block. Seal is dripping oil through a crack, that made it easy to identify where the oil was coming from . Anything else I should do while I have it apart? Should I replace the coil just because it's 30 years old? It works fine. What about the magnets on the flywheel, should I drop some extra JB weld on them?

I wouldn't replace the coil. If its good its good, don't mess with it. Wouldn't hurt to put some JB on the magnets, just make sure that you don't get any on the face of the magnets.

[J-Mech]

On coil: your choice. I wouldn't.

On flywheel magnets: not unless they are loose. Check them out good. DO: clean it up good.

[j4c11]

Originally Posted by J-Mech

On coil: your choice. I wouldn't.

On flywheel magnets: not unless they are loose. Check them out good. DO: clean it up good.

Thanks Jonathan, I'll give it a good scrub down.

[j4c11]

My seal arrived in the mail yesterday and so today I proceeded to pull the leaky one out. Once I did, surprise another seal right behind it. Full of surprises this engine is.

Since I had the valve covers off I decided to check the clearance. As a side note, I've been trying to find some information on valve clearance and how it affects the engine and I haven't been able to find a clear writeup, especially in relation to small engines. I wish someone here with the knowledge would do a technical writeup on valve clearance, theoretical reason behind it, what it does, how increasing and decreasing it affects the engine. But anyway, there's no clearance on the intake valves, 0. The manual says 0.003/0.006, and it looks like the Magnum valves are not adjustable, you have to take it out and grind it. Those things looks like a major PITA to take off and put back on, is it worth the trouble to take them off , the engine runs ok but again, I'm not sure what the impact of that tiny gap of 0.003 is.

[J-Mech]

Not really much of a tech write up......

Valve clearance is easy. The clearance is so that the valve always shuts all the way. Internal engine parts get hot and expand. If there isn't a gap between the cam and the valves when cold, then when the engine gets hot the expanded parts would hold a valve open. That is why most exhaust valve clearances are wider than the intake. Exhaust valves get hotter. The amount of gap is set so that the tolerance is close at rated engine temps... but not touching. If gap is too wide, then it works just like a hammer hitting a punch. Eventually, it will mushroom the end of the valve. If gap is too close, it will hold the valve open when the engine gets hot.

So.... when you ask if it's worth it to get the gap correct..... YES. Now, on your mag motor, it's not adjustable. Yes, you have to grind the valve stem to set clearance if it is too tight. However, those motors spec range is very wide. I suppose you could do it on your own, but it is better to use a valve grinder to "trim" the stem. It needs to be perfectly flat because if not, as the pushrod hits the valve, it needs to hit squarely or it will "beat" it flat and the gap will be too wide. If you have a bench grinder, you could set up the steady rest so that you can hold the valve on the side of the wheel. Also, you would need to get a very fine grit, soft stone. You would need to check it with a square to be sure that the rest and wheel are at a 90 deg angle.

Make sense?

[timbo2]

Was the piston in the right position when you measured?

Getting the valves out isn't bad if you have compression tool. getting the little keepers on during reassembly can be tricky but the mags are easier than the k series to me.

[J-Mech]

Originally Posted by j4c11

I'm not sure what the impact of that tiny gap of 0.003 is.

The spec is .003" - .006" on intake. Exhaust depends on SN of the motor.

[j4c11]

Thanks Jonathan. Seems like a valve grinder is a fairly expensive piece of equipment, especially for a one time job. It also seems like you can't just take the valves to someone, they'd have to have the whole engine to get the gap right. So how is this typically accomplished, you take the whole engine to a shop?

Timbo2, I measured at TDC on the compression stroke, couldn't get even the thinnest feeler in. The exhaust is at 0.008, out of spec as well.

[J-Mech]

Yes, you would take the whole motor. Going that far, I would go ahead and do a valve job. Unless the parts are shot, it really shouldn't take much money or time. No 3 angle stuff... just give it a new sealing surface and lap them.